The invention relates to the formation of expansion joints in a settable surface covering composition such as concrete as commonly used in the construction industry for sidewalks, airport runways and taxiways, roadways, building floors, decks, patios, etc. More particularly, it relates to a two-piece joint-forming device that can be implanted in a settable composition during the plastic stage, with one piece later removed to form a joint filled with a permanent, pliable joint material which effectively accommodates slab expansion and contraction. The invention also encompasses a method for forming a slab joint.
Such joints in most settable compositions such as concrete are necessary in order to prevent surface cracks due to expansion or contraction of the composition during curing and later on due to environmental temperature variations. In the prior art it has been known to use a joint former structure made of a plastic material formed as two portions connected by a severable web. Such a structure, as shown in U.S. Pat. No. 3,330,187, was inserted in freshly poured concrete mix and when the concrete had hardened an upper portion was severed from the lower portion buried in the concrete, thereby forming a surface groove. Although the aforesaid structure provided good results in many installations, as when used between masonry or terrazzo tiles, it was difficult to use with efficiency in the construction of large concrete slabs, such as roadways, aircraft runaways and the like. The problem arose because this prior joint forming structure was too flexible and would bend or flex when forced vertically into freshly poured concrete. Thus, it became very difficult to maintain adequate straightness for the joint grooves without the use of additional equipment, time and labor. Also, in the aforesaid joint structure the top portion once severed from the bottom portion became a waste product and was not reuseable. This not only increased its relative cost but also created a waste disposal problem.
In my U.S. Pat. No. 3,838,930 is disclosed two-piece joint forming structure in which a top portion is removable from the bottom portion and reuseable. The pliable bottom portion remains below the surface of the slab, with a permanent groove in the slab positioned thereabove.
U.S. Pat. No. 3,923,411 discloses a generally V-shaped sealing strip for use in sealing a pre-existing joint between concrete slabs. The device does not form joints in freshly poured compositions, and the two sides of the "V" are firmly locked and sealed together near the top following installation of the device.
While several of the devices discussed above are effective in causing shrinkage cracking and thermal cracking to occur at the joint, and are relatively efficient in preventing the intrusion of water downwardly through the joint, none provides as effective a water seal in an integrally formed joint, especially during expanded and contracted periods, as does the joint-forming device of the invention as described below.